Radiation detectors



Jan 29, 1963 E. F. DALY RADIATION DETECTORS Filed Jan. 15, 1960Inventor" Em FRANK 0m 3,075,386 RADEATIQN DETECTOR Edgar F. Daiy,Cambridge, Engiand, assignor to Unieam Instruments Limited, Cambridge,Engimd, a company of Great Britain Filed Jan. 15, 1960, Ser. No. 2,623Claims priority, application Great Britain Earn. 27, 1959 7 Claims. (Cl.73-355) The present invention relates to radiation detectors, and moreparticularly to dectors of radiation, such as infrared radiation, whichoperate by means of a thermal mechanism, the radiation being incident ona receiver which is thereby raised in temperature. In a thermocouplethis rise in receiver temperature is transmitted to a thermoelectricjunction and a thermoelectric voltage results which may be observed by agalvanometer or other indicating device, if necessary afteramplification. In a bolometer the rise in temperature causes aresistance change in the receiver and this in turn gives rise to achange in current when a given voltage is applied, the change in currentbeing registered on an indicating device.

One of the difliculties in constructing thermocouples and bclometershaving high sensitivity in the long Wavelength infrared and microwaveregions is that of securing efiicient absorption of incident radiationby the receiver. Hitherto a coating of a black material, such as a layerof gold evaporated in a pressure of a few millimetres of nitrogen hasbeen used to give the receiver high absorbing power. However, to beefiective such a black coating must have surface irregularities of thesame dimensions as the wavelength of the incident radiations and musttherefore become so thick for long wavelength absorption that thethermal capacity is unduly increased.

Another absorption mechanism is possible which is not wavelengthsensitive in this way. In this mechanism a thin conducting film ofappropriate resistance intercepts the radiation and absorbs it in amanner similar to that of the appropriate resistive termination of acoaxial cable or waveguide for microwave frequencies.

According to the present invention a radiation detector comprises a thinsupporting sheet or film of electrically insulating material carrying onone surface an absorbing electrically conducting film for interceptingand absorbing incident radiation and carrying on its other surface asecond electrically conducting film opposite to the first film andserving to receive heat transmitted thorugh the insultaing support fromthe first film, said second electrically conducting film forming part ofa thermocouple or bolometer.

The insulating supporting material preferably consists of a thin film ofa material such as collodion, i.e. a nitrocellulose compound soluble ina mixture of alcohol and ether, or Formvar.

The absorbing film is constructed so as to have an appropriateresistance to intercept the radiation and absorb it at the operatingtemperature of the radiation detector and may be made of metal, forexample, of aluminum, gold or nickel, or of a semi-metal such asbismuth, or a semi-conductor such as selenium or tellurium.

Where the receiver film is to form part of a thermocouple, it may bemade for example of gold and the points of two wires of thermoelectricmaterials may be placed in contact with the receiver film to form thehot junction of a thermocouple. Where the receiver film is to form partof a bolometer, it may make contact with metal electrodes carried by theinsulating support and which are themselves connected to wire throughwhich an electric current may be fed.

in order that the invention may be more fully under- 3,fi75,38fiPatented Jan. 29, 1963 stood reference will now be made to theaccompanying drawing, in which:

FIGURE 1 is a diagram representing a section through a radiationdectector according to the invention in the form of a thermocouple.

FIGURE 2 is a plan view of the device in FIGURE 1,

FIGURE 3 is a diagram representing a section through a radiationdetector according to the invention, in the form of a bolometer, and

FIGURE 4 is a plan view of the device in FIGURE 2.

Referring to FIGURES l and 2, the device is of genrally cylindrical formand comprises an annular support 1 over one end of which is mounted avery thin plastic film 2 made of collodion. A rectangular area 3 ofabsorbing metal is deposited on the outer surface of the collodion film,for example by evaporation of aluminum, and on the opposite surface ofthe collodion film is formed a metallic receiver element 4 over'an areacorresponding to the area 3, and consisting of a layer of gold depositedby evaporation. The opposite end of the annular support to that carryingthe collodion film 2 is closed by an insulating cover 5 through whichextend two wires 6 and 7 of thermoelectric materials having sharp points6a and 7a which are in contact with the gold receiver film 4 and arelightly welded to it by a condenser discharge Welding process. Heatabsorbed by the aluminum absorber film 3 is then transmitted through thebase plastic film 2 t0 the gold receiver film 4, the temperature ofwhich rises. The gold receiver film 4 and the two point contacts 6a and7a of thermoelectric materials form the hot junction of a thermocouple.

In the embodiment of FIGURES 3 and 4, an annular insulating support llhas positioned over one end a very thin plastic film 12 of collodion onone surface of which is deposited an area 13 of absorbing metal film,for example by evaporation. This film may consist of gold or nickel. Theopposite surface of the insulating film carries a receiver film 14-which extends over and beyond the area of the film 13 on which radiationis to be received, and is connected to electrodes 15 formed by metaldeposits. Connecting wires K6 are connected with the electrodes 15 sothat an electric current can be fed through the receiver film, changesin the current or voltage being observed with changes in the incidentradiation on the receiver film 13.

The present invention provides a radiation detector which has highsensitivity over a wide spectral range including the long wavelengthinfra red and microwave re gions and which can be used over atemperature range extending from room temperatures down to liquid airtemperatures.

It will be understood that the conducting film can be formed of othersubstances besides those specifically mentioned which are given solelyby way of example.

I claim:

1. A radiation detector comprising a thin supporting film ofelectrically insulating material carrying on one surface an absorbingelectrically conducting film for intercepting and absorbing incidentradiation and carrying on its other surface a second electricallyconducting film opposite to the first electrically conducting film andserving to receive heat transmitted through the insulating support fromsaid first electrically conducting film, said second electricallyconducting film forming part of an electrical detecting circuit.

2.. A radiation detector as claimed in claim 1, in which the insulatingsupporting material consists of a thin film of collodion.

3. A radiation detector as claimed in claim 1, in which the heatreceiving film is to form part of a thermocouple and has the points oftwo Wires of thermoelectric ma- 3 te'rials placed in contact with saidfilm to form the hot junction ofthe thermocouple.

4. A radiation detector as'clairned in claim 1, in Which the heatreceiving film is to form part of a bolometer and makescontact withmetal electrodes carried by the insulating support and which arethemselves adapted to be connected-to v'vi're's through which anelectric current can befed 5. A radiation detector as claimed inclaim1', comprising an annular support over oneend of which is mounted thethin-film of'ifisulatin'g material carrying the absorbing film andth'eheat-receiving film respectively on its opposite surfaces. 7

6-A-radiation detector comprising a support, a thin film of electrically'insulating' material carried by said silpport,'- aradiationab'sor'oing metallic layer for interceptingandabsorbing incidentradiation on one surface of the film of ins-ulating'material, a secondmetallic layer" on the opposite" surface ofthe insulating film oppositethe first metallic layer and servingto' receiveheattransmittedth'r'ough' the insulating support'from' the first layer 7and-two poinf-contacts'of thermoelectric material in con- 4. tact withsaid second layer, said contacts forming the hot junction of athermocouple.

7. A radiation detector comprising a support, a thin film ofelectrically insulating material carried by said support, a radiationabsorbing metallic layer for intercepting and absorbing incidentradiation on one surface of the film of insulating material, asecond'metallic layer on the opposite surface of the insulating film oppositethe first metallic layer andserving to receive heat transmitted throughthe insulating support from the first layerand spaced metal electrodesin contact with saidsecondlayer and arranged so that it acts as abolometer.

' References Cited in 'the file of this patent UNITED STATES PATENTS2,526,491; Liston Oct. I7, 1950 2,587,674 Aiken Mar. 4', 1952 2,728,835Mueller Dec. 27, 1955' 2,824,235 Hahn Feb. 18,- 1958 2,879,424 GarbunyMar. 24, 1959 2,935,711 Christensena -;a-..; -a May 3 1960

1. A RADIATION DETECTOR COMPRISING A THIN SUPPORTING FILM OFELECTRICALLY INSULATING MATERIAL CARRYING ON ONE SURFACE AN ABSORBINGELECTRICALLY CONDUCTING FILM FOR INTERCEPTING AND ABSORBING INCIDENTRADIATION AND CARRYING ON ITS OTHER SURFACE A SECOND ELECTRICALLYCONDUCTING FILM OPPOSITE TO THE FIRST ELECTRICALLY CONDUCTING FILM ANDSERVING TO RECEIVE HEAT TRANSMITTED THROUGH THE INSULATING SUPPORT FROMSAID FIRST ELECTRICALLY CONDUCTING FILM, SAID SECOND ELECTRICALLYCONDUCTING FILM FORMING PART OF AN ELECTRICAL DETECTING CIRCUIT.